Ceramic paint compositions are generally well known to the skilled artisan. These ceramic paint compositions can be used, for example, to form borders around the edge of glass sheets which are used as windshields, sidelites or backlites in motor vehicles.
Such ceramic paints usually include a mixture of metal oxides which together act as a coloring agent for the ceramic paint. The metal oxides are nonreactive with one another and nonreactive with any elements or compounds they come in contact with while being heated to temperatures up to about 1300.degree. F. The mixture of meal oxides can be controlled so as to get a selected color from the ceramic paint composition. Normally, in automotive applications, the selected color is black.
Such ceramic paint compositions also include a low melting point glass frit which generally melts at a temperature below 1300.degree. F. The low melting point glass frit is the material which bonds the mixture of metal oxides to a glass sheet and ensures that it remains after the glass sheet has been cooled back to room temperature. A vehicle is normally mixed with the metal oxides and low melting point glass to allow the ceramic paint composition to be applied in a paint application process. For example, if the paint application process is a silk screen printing operation, the vehicle may be an organic medium which forms the vehicle for carrying the other materials during the silk screen printing operation.
Many different types of ceramic paint compositions of the above general type are well known to skilled artisans. The exact metal oxides and low melting point glass frit and vehicle selected for such paints is well within the skill of artisans in this area. The manner in which the different materials may be varied in order to achieve the results desired in a particular application is again well within the skill of an artisan.
However, I found that in the situation where a sheet having a ceramic paint thereon was contacted by a fiberglass forming die that ceramic paints of the above described general composition had a great tendency to stick on the fiberglass covered die. It is, of course, obvious that the sheet of glass has to be heated to an elevated temperature, generally less than 1300.degree. F., so that it may be engaged by a forming die and formed into a configuration other than flat.
Thus, the difficulty arose that the ceramic paint compositions generally known to skilled artisans would not operate in a glass forming process in which a heated glass sheet containing the ceramic paint composition was engaged by a fiberglass covered forming die. No other materials are known for covering the forming die because the fiberglass is the only material which will withstand the heat and rigorous requirements of the environment to which it is subjected. Other materials that have been used to cover forming dies quickly break down and wear out when repeatedly brought into engagement with the surface of a healed glass sheet. Thus, fiberglass is the material which is used to cover forming dies and this material unfortunately sticks to the ceramic paint compositions known to skilled artisans when those compositions are heated to an elevated temperature necessary in order to form glass by a forming die.
Thus, the problem presented to me was one of developing a method of forming glass sheets with a ceramic paint thereon which could withstand high temperatures and repeated engagements of painted glass sheets by the same forming die without paint sticking to the forming die. I have solved this problem by the addition of a material to the ceramic paint composition which provides for a nonstick barrier between the heated ceramic paint composition on a heated glass sheet and a fiberglass forming die coming into contact therewith.
No search was conducted on the subject matter of this specification in the U.S. Patent and Trademark Office or in any other search facility. However, I am aware of most prior art in this area because of my extensive work in this area, and I know of no prior art more relevant to this subject matter than that which was set forth above, namely, the general discussion of previously known ceramic paint compositions which could not withstand being engaged by fiberglass forming dies.